The invention relates to blades is based on a blade made from an alloy based on a doped gamma-titanium aluminide and methods for making blades.
EP 0 513 407 B1 describes a blade of an alloy based on doped gamma-titanium aluminide in which the blade foot has a finely-grained structure, and the blade body has a coarsely-grained structure. Because of this, the blade body supposedly has a good creep strength and tensile strength resistance at high temperatures, the blade foot a high ductility. The problem, however, is the fatigue behavior of the blade body that is due to its coarsely-grained structure and the relatively complex blade production.
The invention is based on the task of improving the fatigue behavior and the creep strength resistance in a blade and a method for producing the blade of the initially mentioned type.
According to the invention, this is accomplished by providing a blade comprising a blade body and a blade foot made from an alloy based on doped gamma-titanium aluminide, at least part of the surface layer of the blade having a finely-grained structure, and the core has a coarsely-grained structure, whereby the ductility of the finely-grained surface layer is higher than that of the coarsely-grained core.
According to a further aspect of the invention, a method for producing the blade includes a method for producing a blade, wherein the method comprises casting and hot-isostatic pressing of the blade, and deforming the surface of the blade, wherein the deformed surface layer is subjected to recrystallization annealing.
An important aspect of the invention is therefore that at least part of the surface structure of the blade has a finely-grained structure, and the core has a coarsely-grained structure, whereby the ductility of the finely-grained surface layers is higher than that of the coarsely-grained core.
The advantages of the invention are, among others, that, the combination of coarsely-grained structure in the core and finely-grained structure on the surface of the blade increases the surface ductility and improves the fatigue behavior as well as tensile and creep strength resistance compared to previously known blades. Since the grain-size in gamma-titanium aluminides represents the critical value for fissure growth, the reduction of the grain size on the surface increases the error tolerance and thus improves the useful life of the blade. The thermomechanical fatigue resistance is also improved by the finely-grained surface layer.
It is particularly advantageous to provide only the blade body with a finely-grained surface layer since it is particularly susceptible to thermomechanical fatigue stresses. This makes it possible to increase the useful life of the blade body.